Ca2+/calmodulin-dependence protein kinase II phosphorylates synapsin I. The phosphorylated synapsin I dissociates from synaptic vesicle and causes the release of neurotransmitter. Two forms of Ca2+/calmodulin-dependent protein kinase II have been identified: the soluble form and the synaptic vesicle-associated form. The vesicle-associated form of the kinase functions both as a binding protein for synapsin I and promotes its dissociation from the vesicles. The relationship between these two forms of the kinases is not clear. In the present study, we are attempting to use mass spectrometric techniques to structurally characterize these two forms of kinases by measuring their masses and obtaining their peptide maps.